Tension equalizing control system



June 21, 1966 J. w. DRENNING 3,257,086

TENSION EQUALIZING CONTROL SYSTEM Filed Aug. 2, 1963 FIGI n 8 I0 2 UTILIZATION L v Q APPARATUS l I 4 i l W W I DRIVE TACHO METER E 2| [2 23 22 l M r Q l ll l4 1 l3 BRAKE RATIO TACHOMETER URCUH' I2 CONTROL MEANS INVENTOR. JOHN W. DRENNING M ATTORNEYS production.

United States Patent "ice TENSION EQUALIZIN G CONTROL SYSTEM John W. Drenning, 5721 Loch Raven Blvd, Baltimore 12, Md.

Filed Aug. 2, 1963, Ser. No. 299,610 6 Claims. (61. 242-754) The present invention is directed to equalizing tension in a linear material fed from a spiral supply. Linear material, in many processes, is most conveniently stored in a spiral configuration on a shaft or mandrel. In many situations it is highly desirable and often necessary to establish and maintain constant tension on the material as it is drawn from the supply.

Maintained constant tension in such a traveling material fed from a spiral supply may be desirable in textile technology, where threads or yarns may be unwound from spools or bobbins and fed to weaving or knitting machinery, or where flat textile material in rolls is fed out for further processing. Maintaining constant tension in recording tape fed from a feed reel is a prevalent problem in magnetic and other tape recording and re- In processing webs of paper fed from a roll, constant tension maintenance is extremely important.

The problem of maintaining constant tension is even more important where multiple spiral supplies of a linear material are being fed into apparatus for producing a composite product. In the example mentioned above, where multiple threads or yarns are fed to a machine, not only is constant tension highly desirable, but equal tension on the stock drawn from separate supplies is desirable. Equalized tension at constantly maintained values is highly desirable also in processing webs of paper from supply rolls wherever two webs are plied together to form a composite product. In the manufacture of corrugated paperboard, for instance, tension in the feeding webs is controlled when these are joined to the corrugated liner.

In tensioning linear material drawn from a spiral supply, it is usual to mount the supply for concentric rotation and draw the material off at the periphery. As the stock is used, its diameter constantly decreases so that application of uniform tension on the traveling web requires a constantly decreasing brake torque resisting rotation of the spiral supply. Brake control means are therefore required which vary the torque in proportion to the effective radius from which the linear material is being drawn. Determination of this radius has been a serious problem in the art. Mechanical means have been used which ride against the surface of the spiral supply for this purpose, but much inconvenience attends their use, and in many cases, particularly where heavy supply rolls are employed, breakage of the mechanical engagement elements is a frequent occurrence.

It is, accordingly, an object of the present invention to provide a constant tension control system in which linear material may be drawn from a spiral supply at a preselected tension which is maintained independently of the decreasing diameter of the supply.

The invention will be further described in connection with the drawings wherein:

FIGURE 1 shows in diagrammatic arrangement means for feeding linear material from the spiral supply under constant tension embodying the system of the present invention, and

FIGURE 2 shows representative electrical circuitry employed with the system of FIGURE 1.

As shown in FIGURE 1, a spiral supply 1 of a linear material 2 is mounted on trunnion means 3 for rotation about its axis on shaft 4. The linear material 2 may be flat sheet material, such as paper or textile, or it may 3,257,086 Patented June 21, 1966 be filamentary linear material, such as textile threads or yarns, or other linear material, such as wire. In providing a spiral supply of filamentary linear material, successive helixes may be arranged in overlapping relationship to form the spiral supply. In this instance, the radius of the spiral supply will remain generally constant as each helix is fed off, the radius decreasing discontinuously as one helix is exhausted and the next is drawn upon.

Draft means is provided for drawing the linear material from the spiral supply 1 comprising a drive motor 6 for rotating a pair of pinch rolls 7 and 8, between which the material 2 is frictionally engaged. On the rotation of the drive motor 6, therefore, the material 2 is drawn off the spiral supply 1. The drive motor 6 is normally energized for rotation at a selected speed which is the primary controlling parameter for the linear speed of the material delivered.

In handling linear material, it is further necessary to provide a control tension against which the draft means operates. The tension developed in the traveling material in its pass from the spiral supply to the draft means is controlled by a brake applying a controllable torque operating to resist the rotation of the supply as the material 2 is drawn from its outer periphery. The brake is shown diagrammatically at 11 in FIGURE 1, and is mechanically connected by coupling 12 to apply the necessary torque to supply 1. In practice, the supply 1 may be a roll of paper aifixed to a shaft 4 to which the braking torque may be applied by brake 11.

The characteristics of brake 11 are important to the operation of the system, which is of the open loop type and does not measure the tension it establishes. Fading of the brake with continued use is undesirable, but its avoidance with mechanical equipment is possible but expensive. Fading is not a serious problem with an eddy .current brake, but at very low or zero r.p.m., little or no restraint is exerted. Particularly with large, heavy rolls of sheet material, it is a practical necessity to have the brake operative when the spiral supply is stationary. Consequently, by far the most preferable type of brake for use with the system of the invention is the magnetic particle brake, which embodies the desired characteristics in quite economic structure.

Representative of the types of brake structures preferably employable in the system of the present invention are those shown in United States Patents 2,685,947, 2,709,507 and 2,840,206. The controlling magnetic field in the magnetic particle brake is generated by a coil which constitutes an electrically responsive control'means which determines the braking torque in dependency on the applied voltage. The coil may be energized by a variably selectable DC. voltage.

In the system of FIGURE 1, the electrically responsive control means for brake 11 is shown at 12 and is energized by control voltage generated by a ratio circuit 13. Ratio circuit 13 is in turn responsive to a first electrical signal varying proportionally with the speed at which linear material 2 is delivered through the draft means, and a second electrical signal proportional to the speed of rotation of stock supply 1. These voltages, as combined in the ratio circuit, supply a signal to the brake control means varying with the speed of the linear the tachometer to shaft means 4 afiixed to the supply.

The tachometer output is a DC. voltage varying linearly.

Withthe speed of rotation of spiral supply 1. Therefore, as the radius of the stock supply decreases With continued delivery, the magnitude of the output signal from tachometer 14 increases proportionally with decrease in radius to provide an output control signal in accordance with the speed of rotation of stock supply 1.

The other control voltage applied to the ratio circuit 13 may, in the embodiment of FIGURE 1, be generated by a similar tachometer 15 rotationally driven by pinch rolls 16 and 17 engaging the linear material between the stock supply and the draft means. The output of tachometer 15 is, as described in connection with tachometer 14, a DC. voltage of a magnitude proportional to the velocity of the linear material.

I In some installations, a velocity indicating voltage of the same type is available as an operating voltage in the draft means, and where this is available, the tachometer 15 is unnecessary. In the arrangement of FIGURE 2, switch 20 may be provided to supply the same control voltage to ratio circuit 13 in lieu of the output from the tachometer 15. In the arrangement of FIGURE 1, drive motor 6 comprises a variable speed direct current motor having a constant voltage field supply 21 and an armature energized by an adjustable DC. voltage source at terminals 22 and 23. Since the armature supply source voltage itself constitutes a parameter whose variations vary with the speed of the material passing through the draft means where the tension is equalized by the present system, this voltage itself, or a constant fraction thereof, may be directly supplied to ratio circuit 13 for the purposes aforesaid.

In the system of FIGURE 1 as specifically described above, the control voltages generated in dependency on the speed of the linear material and the rate of revolution of the spiral supply are unipolar D.C. voltages of an amplitude proportional to the quantity indicated. Obviously,

other forms of sensing voltage could be employed, such as those obtained by using small alternators to supply uniform amplitude output signals whose frequencies are respectively characteristic of the values to be determined. In such illustrative system, ratio circuit 13 could be similarly energized by the outputs of frequency discriminator circuits responsive to the respective variable frequency alternators.

The ratio circuit of FIGURE 1 is designed to supply the desired output signal to brake 11 as described above. It may comprise any of many suitable networks, an example of which is shown in FIGURE 2 of the drawings.

The ratio circuit of FIGURE 2 operates to develop the necessary brake torque on the spiral supply in response to the control voltages fed to its inputs from tachometers 14 and 15. The negative leads from these tachometers are connected in common to terminal 31, while the positive potential from tachometer 15 is supplied at terminal 32, with the positive potential from tachometer 14 supplied to terminal 33. Resistor 34 and resistor 35 are connected across tachometer 15, and a motor driven variable po-' tentiometer 36 is connected across the output from tachometer 14. Relay 37 is connected between the junction of resistors 34 and 35 and brush 38 of potentiometer 36.

Motor 39 is connected mechanically to brush 38 and energized by the operation of relay 37 to drive brush 38 of the potentiometer to the position at which the relay 37 has zero voltage across it, or a voltage lying in a restricted range about zero. In this operation, the motor may be energized from a neutral source terminal 40 and either a negative source terminal 41 or a positive source terminal 42. The motor drives in reverse directions, depending upon the polarity with which it is energized. Relay 37 controls the polarity of this energization in selectively closing contacts 43 or 44 in dependency on the direction of current through the relay coil, provided the same is above the balanced range. Within the balanced range around zero potential across relay 37, contacts 43 and 44 are both open. The motor circuit is poled to drive brush 38 in the correct direction to decrease toward zero whatever potential is developed across the coil of relay 37.

In the circuit of FIGURE 2, potentiometer 36 is provided with a linear resistance element so that the resistance between point 45 and brush 38 is a direct function of brush angle. Consequently, the angular position of brush 38 is the analog of the desired control voltage applied to brake 11 of FIGURE '1. In the circuit of FIGURE 2, the actual control voltage applied to the brake is developed from a variable transformer 50 provided with brush 51 mechanically driven from the shaft of motor 37, and provides an output voltage proportional to the brush angle. Transformer 50 is energized at ter- .minals 52. The controlled output voltage is adjustable in magnitude by a manually settable autotransformer 53 to adjust the system to the desired tension in material 2. The control potential is rectified in bridge 54 to deliver an output voltage E12 to the control means 12 for brake 11.

As will presently appear, the values of the components of the ratio circuit of FIGURE 2 are selected in accordance with the characteristics of the mechanical system characteristic to provide the desired output signal at E12.

Operation of motor 39, under control of relay 37, depends on the ratio of voltage E14, a function of the rotational speed of the spiral supply, to voltage E15, a function of the velocity of the linear material. When the circuit is in equilibrium, the voltage across resistor 35 is equal to the voltage developed in the portion of potentiometer 36 lying between connection 45 and brush 38. Taking this portion of the resistance 36 as r36 and the total resistance of potentiometer 36 as R36, the voltage between connection 45 and brush 38 is E14 [r36/R36]. The voltage developed across resistor 35 is E15 Since these twovoltages are necessarily equalized and balanced by the circuit, we have the following equation:

Resistance r36 is, however, the controlling parameter determining the magnitude of potential E12, as follows: E12=Kr(r36), where Kr is a constant.

Therefore, the output control voltage is-as follows:

It will therefore be seen that the control voltage applied to brake 11 and the consequent torque applied to the spiral supply is proportional to the product of the ratio of the output of speed responsive tachometer 15, divided by a voltage proportional to the rate of revolution of the spiral supply as generated by tachometer 14, multiplied by constant factor. This constant factor is determined by the values of resistor and potentiometer elements 34, 35 and 36, together with factor Kr, which represents the mechanical coupling ratios between brush arm 38 and variable transformer brush arm 51 taken in connection with the energization voltage for transformer 50 applied at terminals 52 and the setting of autotransformer 53. The value of this constant factor is designed in relation to the constants of the mechanical system, as will now appear.

Referring back to FIGURE 1, the delivery velocity of material 2 is conveniently taken as V under a desired tension T. Under these circumstances, the rotational speed of the spiral supply (or rpm.) is N V/ 21rr.

The radius r represents the radius of the spiral supply to its periphery at the point of delivery of the material into its flight to the draft means.

The tension T is desired to be equalized, and its value is T=t/ r. Y

The brake torque t is a function of the magnitude of the input control signal to the control means 12 of brake 11, which may be expressed as t=K12El2, K12 being a constant. We then have the equation: E12: (rT)/ K 12. Since r==V/21rN, the following relation exists:

However, the speed of rotation of the spiral supply is measured by the voltage E14 so that N =E14Kl4. The material velocity V is measured by the output of tachometer 15 which supplies a voltage E15/Kl5=V. As a result of substitutions in the above, it is clear that the desired brake control voltage is as follows:

E12: [BIS/E14] [TK14/21rK12K15] In order to obtain this voltage E12 as the desired output of the circuit of FIGURE 2, it is only necessary to establish the pertinent parameters of the latter in accordance with the following equation:

Similar design procedure may be employed for other ratio voltage type circuits. As will be understood from the earlier discussion, instead of using voltage E15 derive-d from a tachometer 15, an armature supply voltage for the draft means may be substituted therefor from terminals 22 and 23 in FIGURE 1. Such a substitution will merely change the constant K15 to a new one, K15.

While the system, as described, has emphasized the brake torque adjustment to compensate for varying diameter of the stock supply, it may be noted that constant tension is developed despite linear speed variations in the material under varied energization of draft motor 6. As the linear speed of the material approaches zero, the voltages E15 and E14 from tachometers 15 and 14 maintain the same ratio to hold the tension constant and to leave the spiral supply under rotational constraint when delivery is stopped. Where the voltage B15 is derived from the armature winding of draft motor 6, similar conditions obtain whether the excitation voltage is reduced to zero to stop delivery; or the energization circuit opened to permit the system to coast to a stop. In the latter operation, the back generated in the armature provides the necessary control voltage for ratio circuit 13.

Constant tension control systems constructed according to the principles of the present invention are simple, trouble free and stable in operation. The scope of the instant invention will 'be understood with reference to the appended claims.

I claim:

1. Apparatus for a tension equalizing control system for feeding linear material from a spiral supply comprising: means for supporting a spiral supply of material for rotation under feed of said material from the supply, circuit means for generating an electric signal varying proportionally with the speed of rotation of said supply; brake means coupled to said supply and having electrically responsive control means, said brake means being operative to constrain said supply from any rotation upon energization of its control means in the absence of feed; circuit means for supplying an electric signal varying proportionally with the linear speed of said material under feed; and ratio circuit means operative responsively only to both said circuit means to supply a control signal to the electrically responsive brake control means to maintain constant material tension by decreasing the brake torque on the supply as material is fed off and including means for maintaining said control signal at its effective valve as and after feed of the material is stopped.

2. A tension equalizing control system' for feeding linear material from a spiral supply comprising means for supporting a spiral supply for rotation, means for generating an electric signal varying proportionally with the speed of rotation of said supply; brake means coupled to said supply and having electrically responsive torque control means, said brake means being operative to constrain said supply from any rotation upon energization of 6 its control means in the absence of feed; draft means receiving said linear material from the periphery of said supply operative to feed the material continuously therefrom; means for generating an electric signal varying proportionally with the linear speed of said material as it is fed from the supply to the draft means; and ratio circuit means operative responsively only to both generating means to supply a control signal to the electrically responsive brake control means to maintain constant material tension by decreasing the brake torque on the supply as the material is fed off and including means for maintaining said control signal at its effective value as and after feed of the material is stopped.

3. The system of claim 2 wherein the brake means comprises a magnetic particle brake.

4. A tension equalizing control system for feeding linear material from a spiral supply comprising means for supporting a spiral supply for rotation, means for generating an electric signal varying proportionally with the speed of rotation of said supply; brake means coupled to the supply and having electrically responsive control means, said brake means being operative to constrain said supply from any rotation upon energization of its control means in the absence of feed; draft means receiving said linear material from the periphery of said supply operative to feed the material continuously therefrom; means for generating an electric signal varying proportionally with the linear speed of said material as it is fed from the supply to the draft means; and circuit means operative responsively only to both generating means to supply a control signal proportional to the ratio of the output of the second generating means to the output of the first generating 1 means to the electrically responsive control means to maintain uniform material tension between the spiral supply and the draft means and to supply thereto a continuous effective energizing voltage as and after feed of the material is stopped.

5. Atension equalizing control system for feeding linear material from a spiral supply comprising means for supporting a spiral supply for rotation, means for generating an electric signal varying proportionally with the speed of rotation of said supply; magnetic particle brake means coupled to the supply and having electrically responsive control means, said brake means being operative to constrain said supply from any rotation upon energization of its control means in the absence of feed; draft means receiving said linear material from the periphery of said supply operative to feed the material continuously therefrom; means for generating an electric signal varying proportionally with the linear speed of said material as it is fed from the supply to the draft means; ratio circuit means comprising a pair of connected impedance means sepa rately energized in the same polarity only by the respective generating means; motor means operative responsively only to the difference between a predetermined fraction of the voltage applied to one impedance means and a variable fraction of the voltage applied to the other impedance means to equalize the magnitudes of said fractional voltages; and variable voltage supply means responsive to motor movement operative to energize the electrically responsive control means to control brake torque and to maintain a continuous energizing voltage as and after feed of the material is stopped to constrain said supply from any rotation in the absence of feed.

6. A tension equalizing control system for feeding linear material from a spiral supply comprising means for support-ing a spiral supply for rotation, means for generating an electric signal varying proportionally with the speed of rotation of said supply, magnetic particle brake means coupled to the supply and having an electri cally responsive control means, said brake means being operative to constrain said supply from any rotation upon energization of its control means in the absence of feed, variable speed draft means receiving said linear material from the periphery of said supply opera-tive to feed the material continuously therefrom, means for generating an electric signal varying proportionally with the linear speed of said material as it is fed from the supply to the draft means, ratio circuit means comprising a first resistive element connected only with oneoi said generating means, a second resistive element connected only with the other of said generating means, means connecting ends of said two resistive elements of the same polarity together, a movable brush mounted for slidable engagement along one resistive element, motor means drivably connected with said brush, relay means operative to energize said motor means responsively to the potential difference between the remote end of the other resistive element and said brush to activate said motor means to reduce said potential to a substantially null value, and variable voltage supply means responsive to movement of said motor operative to energize the electrically responsive control means to control brake torque to maintain uniform material tension between the spiral supply and the draft means and to maintain a continuous energizing voltage as and after feed of the material is stopped to constrain said supply from any rotation in the absence of feed.

References Cited by the Examiner UNITED STATES PATENTS 2,011,371 8/1935 Mohler 24275.51 X 2,339,939 1/1944 Michel 24275.51 X 2,469,706 5/ 1949 Winther 242-75.5l 2,975,991 3/1961 Michel 24275.51 2,995,968 8/ 1961 Tomberg 242-75 .44 3,018,978 l/1962 Graneau et al. 24275.5l

STANLEY N. GILREATH, Primary Examiner.

M. STEIN, D. E. WATKINS, Assistant Examiners. 

1. APPARATUS FOR TENSION EQUALIZING CONTROL SYSTEM FOR FEEDING LINEAR MATERIAL FROM A SPIRAL SUPPLY COMPRISING: MEANS FOR SUPPORTING A SPIRAL SUPPLY OF MATERIAL FOR ROTATION UNDER FEED OF SAID MATERIAL FROM THE SUPPLY, CIRCUIT MEANS FOR GENERATING AN ELECTRIC SIGNAL VARYING PROPORTIONALLY WITH THE SPEED OF ROTATION OF SAID SUPPLY; BRAKE MEANS COUPLED TO SAID SUPPLY AND HAVING ELECTRICALLY RESPONSIVE CONTROL MEANS, SAID BRAKE MEANS BEING OPERATIVE TO CONSTRAIN SAID SUPPLY FROM ANY ROTATION UPON ENERGIZATION OF ITS CONTROL MEANS IN THE ABSENCE OF FEED; CIRCUIT MEANS FOR SUPPLYING AN ELECTRIC SIGNAL VARYING PROPORTIONALLY WITH THE LINEAR SPEED OF SAID MATERIAL UNDER FEED; AND RATIO CIRCUIT MEANS OPERATIVE RESPONSIVELY ONLY TO BOTH SAID CIRCUIT MEANS TO SUPPLY A CONTROL SIGNAL TO THE ELECTRICALLY RESPONSIVE BRAKE CONTROL MEANS TO MAINTAIN CONTANT MATERIAL TENSION BY DECREASING THE BRAKE TORQUE ON THE SUPPLY AS MATERIAL IS FED OFF AND INCLUDING MEANS FOR MAINTAINING SAID CONTROL SIGNAL AT ITS EFFECTIVE VALVE AS AND AFTER FEED OF THE MATERIAL IS STOPPED. 